Process performance
The main raw material, methanol, should possibly be the pure rectified synthetic product, with assay over 99.85 %. However also some less pure methanol qualities may be economically used, provided that the water content be not higher than 8 % and the polymerizable substances and the chlorine contents be rather low (less than 0.01 %).
Urea should be the pure prilled product of the market, with free ammonia under 0.1 %, and total nitrogen content over 46%.
1. For producing 370 Kg of formaldehyde, in aqueous solution, are needed:
| methanol (100 %) |
425 Kg
|
| electric power (380 to 440 V) |
70 kWh
|
| cooling water (at 28°C max) |
410,000 kCal
|
| cooling water (at 15°C max) |
130,000 kCal
|
| process water (softened) |
300 Kg
|
| condensate or demineralized water |
700 Kg
|
| catalyst cost |
less than 2.6 US$
|
For operating the pneumatic valves are also needed 30 Nm3/h of compressed air at 6 bar, free from oil, dust and moisture.
The molten salts, used as heat transfer medium, employed for cooling the reactor catalyst tubes, is rather stable and needs a partial replacement every four or five years. The cost of such replacement is negligible.
The plant is automatically controlled and may run for many hours without attendance. It is advisable that one operator shall be present for 2 shifts/day, and that during the third shift one operator shall be available only if some trouble should be signalized by the controlling computer. A further reduced attendance may be foreseen during weekends.
2. For producing 370 kg of formaldehyde in urea-stabilized concentrated solution, are needed the same raw materials and utilities as above, (but for the process water, which is not needed) and also:
| urea (100 %) |
about 159 Kg
|
| caustic soda (48 %) |
about 2 Kg
|
The given consumption figures have to be taken with a tolerance of +/- 1 % for the raw materials and of +/- 5 % for the utilities.
3. Exhaust gas treatment:
For the catalytic exhaust gas treatment, if necessary, are extra needed (for each 370 Kg of produced formaldehyde):
| electric power |
3 kWh
|
| catalyst |
about 0.3 US$
|
Such catalyst consumption is given as a rough estimation, as its life span is hard to foresee: one load should work for 2-5 years, but this time period is rather uncertain. If desired, the combustion heat of the exhaust gas may be partially recovered, by producing from 50 to 100 Kg of steam for each 370 Kg of produced formaldehyde. Of course to this aim an additional investment is needed.
4. For each 370 Kg of produced formaldehyde, as in aqueous or in urea-stabilized solution, about 700 Kg of saturated steam at up to 1.5 bar are recovered and put at free disposal. In the case that for an economical employ of such steam a higher pressure is required (up to 20 bar), this need is easily obtained, but the specific electric power consumption rises from 70 to 80 kWh for each 370 Kg produced.